Absorbent materials in the form of relatively thin, dense, sheet-like structures resembling heavy weight paper or paperboard are referred to as absorbent boards to distinguish such materials from loose, bulky absorbents such as wood pulp, fluff, and the like. Absorbent boards may be formed of a variety of materials of natural and/or synthetic origin. For example, absorbent boards may be prepared from wood pulp, peat moss, and mixtures thereof, optionally including other components such as reinforcing synthetic textile fibers, binders, surfactants and the like. Such boards are commonly prepared by wet laying a slurry of the solid components of the board on conventional papermaking equipment as described, for example, in U.S. Pat. No. 4,507,122, incorporated herein by reference. Absorbent boards comprising a hydrophilic fibrous material such as rayon or wood pulp and superabsorbent hydrogel polymers may be prepared by a dry process in which the fibrous mixture is mechanically compressed to a high density as described, for example, in U.S. Pat. Nos. 4,340,556 and 4,610,678.
In accordance with the teachings of U.S. Pat. No. 4,507,122, a laminate structure comprising a thin layer of Kraft paper and a heavier layer of a mixture of peat moss and wood pulp is prepared by sequentially depositing the materials from aqueous slurry in a wet process on conventional papermaking equipment. The deposited solids are dewatered, partially dried and compressed to a density of from about 0.2 to 1.0 g/cm.sup.3. The resulting absorbent board is relatively stiff, and flexibility may be increased by mechanical working such as embossing or micro corrugating. The reference further suggests that the flexibility of the board may be increased by slitting.
Mechanical working of stiff absorbent boards to increase the flexibility thereof is also disclosed for example, in U.S. Pat. No. 4,605,402. In accordance with this reference an absorbent board composed of a web of synthetic fibers impregnated with polymeric superabsorbent is compressed and bonded to form a composite structure. As prepared, the structure is relatively stiff and is processed to increase softness and flexibility by micro corrugation and perfembossing.
The use of peat moss in absorbent structures, usually in combination with other absorbent materials such as wood pulp, has been the subject of many recent patents. U.S. Pat. No. 4,473,440 discloses the preparation of a peat moss board by wet laying a slurry of peat moss onto a predeposited layer of Kraft paper, dewatering and conditioning the board to a specific water content, and then densifying the board by calendering to obtain a highly absorbent material. Wetting agents, coloring agents, adhesives and the like, may be incorporated into the system as desired.
U.S. Pat. No. 4,676,871 discloses an absorbent board comprising a mixture of peat moss with from about 1 to 15% by weight polyester staple fibers as a reinforcing material, and treated with a surfactant to enhance wetability. The board is prepared by air laying to form a low density product followed by calendering to a final density of about 0.7 g/cc.
U.S. Pat. No. 4,226,237 discloses a composite absorbent structure for use in sanitary napkins, diapers and the like, comprising a first layer of cellulose fibers, a second layer of a mixture of peat moss and wood pulp, and an optional third layer of additional cellulose fibers. The peat moss layer may be loosely associated or stabilized with adhesives.
U.S. Pat. No. 4,215,692 discloses an absorbent structure comprising a mixture of peat moss with mechanical wood pulp and optionally with other absorbent materials such as long fibered chemical wood pulp, rayon or the like. Although the absorbent structure is first produced in the form of a board by wet laying, the board is subsequently ground to provide a fluffed material for use in the absorbent products.
Other patent references deal with the treatment of peat moss to enhance its properties for use in absorbent products such as bleaching (U.S. Pat. No. 4,170,515), treating with anti-microbials (U.S. Pat. No. 4,618,496), and grafting with polymeric compositions (U.S. Pat. No. 4,305,393).
The present invention is concerned with a novel absorbent structure composed of peat moss, wood pulp, mixtures thereof or other compacted friable absorbent material. It is an object of the present invention to provide an absorbent board of such materials having improved flexibility in at least one direction, while retaining the overall structural integrity of the board. It is a further object of this invention to provide a longitudinal absorbent board comprising peat moss which is highly flexible in its transverse direction and moderately flexible in the longitudinal direction. It is a yet further object of this invention to provide a relatively thin, highly absorbent, highly flexible absorbent element suitable for use as the primary absorbent in sanitary napkins, diapers, and the like. These and other objects of the present invention will be more readily understood from the ensuing description of the invention.